Technical Field
The present disclosure relates to a sealing apparatus, and particularly relates to a sealing apparatus for sealing an annular space formed between two members which are movable relative to each other.
Background Art
Conventionally, a sealing apparatus is used for sealing an annular space formed between two members which are movable relative to each other, for example, an annular space formed between a moving member such as a shaft or a piston and a member such as a housing or a cylinder which covers the moving member on the outer periphery side. FIG. 5 is a partial cross-sectional view showing a schematic configuration of a conventional sealing apparatus of this type. The conventional sealing apparatus 100 shown in FIG. 5 is used in a state in which the sealing apparatus 100 is mounted between an opening 112 of a housing 111 and a shaft 113 so as to seal an annular space formed between the opening 112 of the housing 111 and the shaft 113 inserted into the opening 112 in a manner allowing relative movement. The sealing apparatus 100 includes: a lip member 101 which is made of a resin material such as PTFE (polytetrafluoroethylene) and which has an annular shape about an axis; and a spring member 102 which is made of a metal material and which has an annular shape about the axis. In the lip member 101, an annular outer-periphery-side lip 105 extends toward the high pressure side (the right side in FIG. 5) from an outer periphery side of an end portion of an annular lip base portion 104 on the high pressure side and an annular inner-periphery-side lip 106 extends toward the high pressure side from an inner periphery side of the end portion of the lip base portion 104 on the high pressure side. Accordingly, an annular accommodating groove 103 which is recessed toward the low pressure side (the left side in FIG. 5) in the axis direction is fainted on the lip member 101. As shown in FIG. 6, the spring member 102 is an annular member having a substantially V shape in a cross section, and the spring member 102 is accommodated in the accommodating groove 103. The spring member 102 includes an outer periphery pressing portion 107 extending in an inclined manner from the low pressure side toward the high pressure side and the outer periphery side, and the outer periphery pressing portion 107 comes into contact with the outer-periphery-side lip 105 from the inner periphery side. The spring member 102 includes an inner periphery pressing portion 108 extending in an inclined manner from the low pressure side toward the high pressure side and the inner periphery side, and the inner periphery pressing portion 108 comes into contact with the inner-periphery-side lip 106 from the outer periphery side.
In a usage state of the sealing apparatus 100, the outer-periphery-side lip 105 comes into close contact with the opening 112 of the housing 111, the inner-periphery-side lip 106 comes into close contact with the shaft 113, and the outer-periphery-side lip 105 and the inner-periphery-side lip 106 are pressed in a direction such that the outer-periphery-side lip 105 and the inner-periphery-side lip 106 approach each other by an interference width so that the spring member 102 is compressed. With such a configuration, when the sealing apparatus 100 is in use, the outer-periphery-side lip 105 is pressed against the opening 112 of the housing 111 by a reaction force of the outer periphery pressing portion 107. Further, the inner-periphery-side lip 106 is pressed against the shaft 113 by a reaction force of the inner periphery pressing portion 108. Accordingly, sealing is provided for a space formed between the housing 111 and the shaft 113.
PTFE, which is used as a material for forming the lip member 101, can be used under high temperature and high pressure, and PTFE possesses excellent chemical resistance and oil resistance thus having characteristics suitable for the lip member. However, PTFE plastically deforms easily under high temperature. Accordingly, as described above, the sealing apparatus 100 is equipped with the spring member 102. With such a configuration, even when plastic deformation (settling) occurs in the lip member 101 due to high temperature thus reducing the interference, the spring member 102 presses the lip member 101 and hence, sealing performance of the sealing apparatus 100 is maintained. However, when the sealing apparatus 100 is used at a temperature close to a use limit temperature zone on a high temperature side, due to a difference in coefficient of linear expansion between a metal material for forming the housing 111 and a material for forming the lip member 101, the outer-periphery-side lip 105 is firmly pressed against the housing 111 so that there may be a case in which plastic deformation occurs in the outer-periphery-side lip 105 thus reducing interference of the outer-periphery-side lip 105 with respect to the housing 111. Accordingly, in the sealing apparatus 100, to compensate for the reduction of an interference of the outer-periphery-side lip 105 caused by plastic deformation of the outer-periphery-side lip 105 under high temperature, rigidity of the outer-periphery-side lip 105 is lowered so as to increase the effect (the degree of pressing) of the outer periphery pressing portion 107 of the spring member 102 with respect to the outer-periphery-side lip 105 (For example, see Japanese Patent Application Publication No. 2015-135137).
Recently, there has been demand to reduce fuel consumption of a prime mover such as a vehicle engine or a configuration device of the prime mover such as a driving device for the shaft 113 or the like. In the conventional sealing apparatus 100, an end portion of the spring member 102 on the low pressure side (the left side in FIG. 5) is disposed at a position in which a reaction force of the outer periphery pressing portion 107 and a reaction force of the inner periphery pressing portion 108 are balanced with each other in the accommodating groove 103 and hence, the reaction force of the outer periphery pressing portion 107 cannot be lowered independently from the reaction force of the inner periphery pressing portion 108. Accordingly, as described above, in the conventional sealing apparatus 100, sealing performance can be maintained by reducing an effect of plastic deformation of the outer-periphery-side lip 105. However, when a reaction force of the spring member 102 is reduced so as to reduce friction resistance which is generated between the inner-periphery-side lip 106 and the shaft 113, a contact surface pressure of the outer-periphery-side lip 105 is lowered so that the above-mentioned compensation function with respect to plastic deformation is lowered whereby sealing performance may be declined.
As described above, in the conventional sealing apparatus 100, there has been demand to reduce friction resistance generated in the lip member 101 while suppressing a decline in sealing performance caused by plastic deformation of the lip member 101 when the sealing apparatus 100 is used under high temperature conditions.
The present disclosure is related to providing a sealing apparatus which can reduce friction resistance generated in a lip member can be reduced while preventing a decline in sealing performance.